Preparation of zirconia mullite flakes via a plasma rapid solidification process using starting materials derived from a sol-gel technique

摘要

Flakes of zirconia-mullite with different zirconia contents varying from 3 to 24 wt% were produced from sol-gel derived raw materials via a plasma melting method followed by a rapid solidification process using a rotating copper roll. The morphology, phase constitution and microstructure development of the as-prepared flakes and of the flakes after various heat treatments were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). It was found that the starting materials could be transformed from the initial irregular-shaped powders into flakes which consisted of mullite, zirconia phase, a relatively large amount of glassy phase and pores. Using TEM, it was shown that the crystalline phases consisted of zirconia polymorphs and mullite. The glassy phases consisted of Al2O3-SiO2 solid solution supersaturated with zirconia. Firing at 1500 degreesC or 1700 degreesC resulted in full crystallisation of the flakes and a fairly homogeneous distribution of zirconia particles in terms of size and shape dispersed in the mullite matrix, which contained both intra-granular and inter-granular precipitates. The microstructural characteristics of the flakes may provide promising physical properties for applications in high temperature thermal insulation materials. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 18]